Endocranial morphology of the Brazilian Permian dicynodont Rastodon procurvidens (Therapsida: Anomodontia)

Abstract

Dicynodontia is a major clade of terrestrial tetrapods that greatly diversified during the Permian and Triassic periods, reaching a worldwide distribution. In this study, the endocranial cavity of the Brazilian Permian dicynodont Rastodon procurvidens is described based on a digital endocast obtained using digital imaging (X‐ray computed tomography) and 3D modeling. It was possible to reconstruct the brain, olfactory bulbs, inner ear, some neurovascular canals, cranial nerves, the nasal cavity, and the maxillary recesses. The endocast of R. procurvidens preserves a typical plesiomorphic morphology of non‐mammaliaform therapsids, being predominantly tubular and displaying a relatively short and robust hindbrain. Encephalization quotients (EQs) were calculated for R. procurvidens, resulting in EQs of 0.09 ± 0.03 and 0.13 ± 0.05 (Jerison’s EQ and Manger’s EQ, respectively). Finally, some biological implications of the endocast morphology were inferred for R. procurvidens. Its inner ear is especially small, and its orientation implies a slightly downturned head posture in life. Furthermore, the presence of uncompressed maxillary recesses in R. procurvidens indicates a correlation between the enlargement of the recesses and the reduction of the tusks, also seen in other dicynodonts with reduced tusks.

A redescription of Kunpania scopulusa, a bidentalian dicynodont (Therapsida, Anomodontia) from the ?Guadalupian of northwestern China

“…The single specimen of Rastodon procurvidens from the Rio do Rasto Formation of Brazil (Boos et al, 2016) is the only probable bidentalian record from the Guadalupian so far described; Australobarbarus from the Port Kotel'nich locality of Russia is likely Lopingian in age (Kurkin, 2011;Benton et al, 2012;Sennikov and Golubev, 2017;Kammerer and Masyutin, 2018). As expected, given its phylogenetic position, Rastodon lacks many of the distinctive characters found in later-diverging bidentalians (Boos et al, 2016;Simão-Oliveira et al 2020), and it provides only limited insight into the subsequent diversification of Cryptodontia and Dicynodontoidea. The same is true for other potential basal bidentalians or basal cryptodonts that occur in the Lopingian such as Keyseria or Daqingshanodon (see discussion in Angielczyk and Kammerer, 2017), although the recent discovery of Bulbasaurus from the Tropidostoma Assemblage Zone of South Africa has shed new light on the early history of the Geikiidae (Kammerer and Smith, 2017).…”

Endocranial anatomy of the early prozostrodonts (Eucynodontia: Probainognathia) and the neurosensory evolution in mammal forerunners

“…However, as the braincase of non‐mammaliaform cynodonts was not fully ossified, some regions of the endocast had to be artificially delimited (see Materials and Methods). The rostral limit of the endocast is based on the lateromedially oriented crests on the ventral surface of the frontals since there is no ossified cribriform plate (it was probably cartilaginous in life), a trait shared with all other non‐mammaliaform therapsids (e.g., Bendel, Kammerer, Kardjilov, Fernandez, & Fröbisch, 2018; Franco et al, 2021; Kerber et al, 2021; Kielan‐Jaworowska, Cifelli, & Luo, 2004; Oliveira, Kerber, & Pinheiro, 2020; Pavanatto et al, 2019; Pusch et al, 2019; Rodrigues et al, 2014; Rowe et al, 2011). Hence, we arbitrarily set up the limit of the rostral region of the cranial endocast with a flat cut (Figure 4).…”

Nasal turbinates of the dicynodont Kawingasaurus fossilis and the possible impact of the fossorial habitat on the evolution of endothermy

“…In contrast to Pristerodon , which possessed well‐developed maxillary recesses (Barry, 1967; see also Figures 4 and 6b), the nasal cavity of Kawingasaurus was not expanded by paranasal sinuses. Maxillary sinuses were described from numerous dicynodonts such as Lystrosaurus (Benoit et al, 2018; Cluver, 1971), Diictodon feliceps (Agnew, 1959; Benoit et al, 2018; Sollas & Sollas, 1914), Cistecephalus (Benoit et al, 2018; Keyser, 1973), Rastodon procurvidens (Simão‐Oliveira et al, 2019), Patranomodon nyaphulii , Eodicynodon oosthuizeni , Abajudon kaayai , Compsodon helmoedi , Myosaurus gracilis , and Oudenodon bainii (Benoit et al, 2018).…”

“…More caudally (Figure 2g,h), the mesethmoid became more and more ossified from dorsal to ventral. Median ridges, as possible sites for attachment of a cartilaginous nasal septum, were also described from the dicynodonts Sangusaurus parringtonii (Angielczyk et al, 2018) and Rastodon procurvidens (Simão-Oliveira et al, 2019), and from most cynodonts (e.g., Franco et al, 2021;Kerber et al, 2020;Ruf et al, 2014).…”

“…Simão-Oliveira et al, 2019), Patranomodon nyaphulii, Eodicynodon oosthuizeni, Abajudon kaayai, Compsodon helmoedi, Myosaurus gracilis, and Oudenodon bainii(Benoit et al, 2018).…”